Altitude sickness isn't so much a simple function of altitude, says Tod Schimelpfenig, the curriculum director of Wilderness Medicine Institute in Lander, Wyo. It is more a function of a rapid change from lower to higher altitude - the quicker and the greater altitude gain in the transition, the worse the symptoms.
"Combine quick rise in altitude with aggressive exercise and you've got a problem," he says.
"What's difficult about altitude sickness is that it looks like all kinds of other ailments," says Schimelpfenig. Symptoms include headache, nausea, lack of energy and appetite - your basic flu, he said. Drinking water and especially resting for a few days helps in getting used to a higher altitude, he said, but the only real cure is to drop down to a lower altitude, if symptoms persist.
The Zion/Bryce Canyon area ranges from 3,000 feet in elevation in Zion, to 8,000 and 9,000 feet elevation in Bryce Canyon -- 10,000 feet in nearby Cedar Breaks National Monument. Those higher elevations can trigger altitude sickness.
Schimelpfenig says a more serious altitude-related illness is pulmonary edema, or water on the lungs. Victims can die if they aren't transported right away to a lower altitude, he says.
Rob Wissinger, emergency medical services coordinator for Zion National Park, says altitude sickness at Zion is pretty rare. "When visitors exhibit symptoms, it is usually because they've got the flu."